The present invention relates to a magneto-optic memory apparatus capable of recording, reproducing and erasing information, and more particularly to a magneto-optic memory apparatus which is provided with a defect detector to improve the reliability of recorded data and increase the transfer rate.
A magneto-optic memory apparatus such as a magneto-optic disk apparatus can record, reproduce and erase information, and can be used in place of a large-storage capacity magnetic memory apparatus. In the magneto-optic memory apparatus, however, it is required to make the direction of magnetic field applied to a recording medium in a recording operation opposite to the direction of magnetic field applied in an erasing operation, and it takes time to reverse the direction of applied magnetic field. Usually, each of the recording and erasing operations is performed in such a manner that a magnetic field is applied to a recording medium in a direction corresponding to the recording or erasing operation, and the recording medium is irradiated with a light beam modulated in accordance with the recording or erasing operation. The above method is called the light modulating method. The operations of this kind are described in, for example, Applied Optics, Vol. 25, No. 4, 1986, pages 483 to 489, and U.S. Pat. application Ser. No. 743,974. A magnetic memory apparatus has an overwrite function, that is, a function of erasing recorded information by writing new information on a track which contains the recorded information. However, a magneto-optic memory apparatus according to the light modulating method does not have the writeover function. Hence, in order to record new information, it is necessary to perform three operations, that is, an erasing operation for erasing information which has been recorded in a region where new information is to be recorded, a recording operation for recording the new information in the above region, and an RAW operation (namely, read-after-write operation) for checking the state of information recorded by the recording operation. In other words, in order to record information, it is required to perform the erasing, recording and RAW operations for the same recording region. The fact that three operations are required to record information, makes it difficult to increase the transfer rate of the magneto-optic memory apparatus.